The present invention relates to optical encoders. More particularly, the present invention relates to optical encoder systems and methods for use in printing devices.
Printing devices, such as inkjet printers, use printing composition (e.g., ink or toner) to print text, graphics, images, etc. onto print media. Inkjet printers may use print cartridges, also known as "pens", which shoot drops of printing composition, referred to generally herein as "ink", onto a print medium such as paper or transparencies. Each pen has a printhead that includes a plurality of nozzles. Each nozzle has an orifice through which the ink drops are fired. To print an image, the printhead is propelled back and forth across the page by, for example, a carriage, while shooting drops of ink in a desired pattern as the printhead moves. The particular ink ejection mechanism within the printhead may take on a variety of different forms known to those skilled in the art, such as thermal printhead technology.
In a current thermal system, a barrier layer containing ink channels and vaporization chambers is located between an orifice plate and a substrate layer. This substrate layer typically contains linear arrays of heating elements, such as resistors, which are energized to heat ink within the vaporization chambers. Upon heating, the ink in the vaporization chamber turns into a gaseous state and forces or ejects an ink drop from a orifice associated with the energized resistor. By selectively energizing the resistors as the printhead moves across the page, the ink is expelled in a pattern onto the print media to form a desired image (e.g., picture, chart or text).
Inkjet printers may depend on a linear displacement optical encoder strip to trigger the firing of the pens as well as to provide feedback for position and velocity of the carriage holding the pens. The optical encoder strip may be made from things such as photo imaged MYLAR brand film. The optical encoder strip works with a light source and a light detector, both of which are typically mounted on the carriage in a single package. The light source directs light through the strip which is received by the light detector and converted into an electrical signal which is used by electronics of the printing device to control firing of the pens, as well as carriage position and velocity. Markings or indicia on the encoder strip periodically block this light from the light detector in a predetermined manner which results in a corresponding change in the electrical signal from the detector.
As the pens eject droplets of ink through the printhead orifices, a certain amount of ink is dispersed within the printing device as aerosol. Print media dust can also be produced within the printing device as the printing device handles print media. This aerosol and dust is contaminant matter that is deposited on the interior surfaces of the printing device and also onto the optical encoder strip. The build-up of these contaminants on the optical encoder strip reduces the amount of light from the light source that reaches the light detector. The optical encoder strip can also become scratched. These conditions can lead to a loss of both information and control of carriage position and velocity, as well as timing associated with pen firing. Several problems can arise from these losses, including degradation of print quality and driving of the carriage into a failure state which causes the printing device to cease to operate.
Alleviation of these problems would be a desired improvement, thereby increasing the useful life of a printing device. Accordingly, the present invention is directed to solving printing device problems caused by both contaminant matter accumulating on printing device optical encoder strips and scratches occurring on optical encoder strips. The present invention accomplishes this objective by providing optical encoder systems and methods for use of these systems in printing devices.
An embodiment of the present invention is an optical encoder system for use in a printing device that includes a dispenser and a take-up mechanism. The dispenser includes an encoder strip which has a first length and a second length. The second length of encoder strip is substantially free of contaminant matter. The first length of the encoder strip is coupled to the take-up mechanism so that the first length of the encoder strip is positioned between the dispenser and the take-up mechanism. The take-up mechanism is configured to advance at least a portion of the second length of the encoder strip from the dispenser to a position between the dispenser and the take-up mechanism upon actuation of the take-up mechanism.
The above-described embodiment of the present invention may be modified and include the following characteristics described below. A cleaner may be included which is configured to remove contaminant matter on the encoder strip during advancement of the encoder strip. The cleaner may include a wiper or a scraper in contact with the encoder strip during removal of the contaminant matter therefrom. The cleaner may additionally or alternatively include a liquid applied to the encoder strip by, for examples one or more pads.
The encoder strip may be formed as a loop which is positioned around the dispenser and the take-up mechanism.
A tensioning device may be included which is configured to keep the encoder strip substantially taut between the dispenser and the take-up mechanism.
A container may be included in which a portion of the encoder strip is placed. The container is configured to keep the encoder strip therein substantially free of contaminant matter and also protects the encoder strip from scratching while in the container. A seal may be positioned between the container and a portion of the encoder strip.
The container, take-up mechanism, and dispenser may be formed as a cassette or a cartridge. The optical encoder system may be used in a printing device.
An alternative embodiment of the present invention for use in a printing device includes an encoder strip and structure for selectively supplying a predetermined portion of the length of the encoder strip to the printing device for use by the printing device during printing. In this embodiment, the encoder strip has a length and the supplying structure supplies to the printing device a predetermined portion of the length of the encoder strip that is substantially free of contaminant matter.
The embodiment of the present invention described in the paragraph immediately above may be modified and include the following characteristics described below. Additional structure may be included for cleaning contaminant matter from the encoder strip. Additional structure may also be included for tensioning the encoder strip. The optical encoder system may be used in a printing device.
An embodiment of a method in accordance with the present invention for use in a printing device includes providing a first length of encoder strip to the printing device for use by the printing device during printing. This first length of encoder strip is substantially free of contaminant matter upon initial provision to the printing device. The method additionally includes removing the first length of encoder strip from use by the printing device and advancing at least a portion of a second length of encoder strip to the printing device for use by the printing device during printing. This second length of the encoder strip is substantially free of contaminant matter upon initial advancement to the printing device.
The above-described embodiment of the method of the present invention may be modified and include the following characteristics described below. The method may include cleaning the first length of the encoder strip to remove contaminant matter therefrom. In such cases, the method additionally includes removing the portion of the second length of encoder strip from use by the printing device and, subsequent to cleaning, advancing the first length of encoder strip to the printing device for use by the printing device during printing.
Other objects, advantages, and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.